Process for the production of record material

Abstract

A color developing material is produced by: a) gradually adding a metal silicate solution to a solution of an aluminum salt which is initially at a pH below 4 until the pH of the resulting mixture is approximately 4, thereby to induce some precipitation and to form a sol; b) gradually adding alkali to said sol to raise the pH to approximately 7, thereby to induce further precipitation and gel the sol or further gel the sol, said gelled sol being a hydrated silica/hydrated alumina composite; c) separating the gel from the aqueous medium and washing the resulting product to remove dissolved salts; and d) drying the washed product and reducing it in particle size. This color developing material is then formulated into a coating composition, applied to a paper base and dried to produce a color developing record material as used in pressure-sensitive (carbonless) copying pape sets.

We claim: 
     
       1. A process for the production of record material carrying a colour developer composition incorporating a hydrated silica/hydrated alumina composite in which hydrated silica predominates, in which process the composite is precipitated from an aqueous medium containing a solution of a metal silicate and an aluminum salt, and a coating composition incorporating the precipitated composite is formulated and then applied to a substrate which is subsequently dried to produce said record material, the process comprising the steps of: (a) gradually adding a metal silicate solution to a solution of an aluminum slat which is initially at a pH below 4 until the pH of the resulting mixture is approximately 4, thereby to induce some precipitation and to form a sol;   (b) gradually adding alkali to said sol to raise the pH to approximately 7,thereby to induce further precipitation and gel the sol or further gel the sol, said gelled sol being a hydrated silica/hydrated alumina composite;   (c) separating the gel from the aqueous medium and washing the resulting product to remove dissolved salts; and   (d) drying the washed product to an extent effective to collapse the structure of the gel and convert the gel structure form a hydrogen to a xerogel, and reducing it in particle size before formulation into the coating composition,   with the proviso that if hydrated zirconia is also present in the precipitated composite, the zirconia content is less than about 10% on a dry basis, based on the total dry weight of alumina, silica and zirconia in the composite.   
     
     
       2. A process as claimed in claim 1, wherein the gelled sol produced in step (b) is subjected to a hydrothermal treatment before being separated and washed as specified in step (c). 
     
     
       3. A process as claimed in claim 1 wherein a hydrated metal oxide is precipitated from a metal salt solution so as to form part of the final composite. 
     
     
       4. A process as claimed in claim 3, wherein the hydrated metal oxide is of zinc, zirconium, copper or nickel. 
     
     
       5. A process as claimed in claim 1 wherein additional hydrated alumina is incorporated in the composite after it has been formed by a secondary precipitation from an aluminium salt solution. 
     
     
       6. A process as claimed in claim 1 wherein the hydrated alumina content of the composite is in the range 6 to 40% by weight, based on the total dry weight of hydrated silica and hydrated alumina. 
     
     
       7. A process as claimed in claim 6 wherein the hydrated alumina content of the composite is in the range 10 to 30%, based on the total dry weight of hydrated silica and hydrated alumina. 
     
     
       8. A process as claimed in claim 6 wherein the alumina content of the composite is about 20%, based on the total dry weight of the composite. 
     
     
       9. A process as claimed in claim 7 wherein the surface area of the composite is in the range 600 to 700 m 2  g -1  and the pore volume is in the range 0.7 to 1.1 cm 3  g -1 . 
     
     
       10. a process as claimed in claim 1 wherein the particle size of the composite is said coating composition is in the range 4 to 6 μm.